does it matter if you give baby bigger dummies?

i bought my baby a new pack of dummies (pacifier) because she seems to prefer certain ones so thought id get extras. When i got home i saw that it said 6-18 months on it. I didnt know you could get different ages, i havent taken them out the pack, but i think the teat on them is very slightly bigger. What is the difference and can i still give them to her? I dont drive and this shop was quite a while away so dont really want to go all the way back to swap them if ibdont need too?? She is 2 months